Electrode starting arrangement having a coiled heating element connected to the retroverted portion of the electrode



Dec. 5, 1967 w. J. DECKER ETAL 3,356,884

ELECTRODE STARTING ARRANGEMENT HAVING A COILED HEATING ELEMENT CONNECTED TO THE RETROVERTED PORTION OF THE ELECTRODE Filed June 50, 1964 FIG.2.

INVENTORS Walter J. Decker and Hugh D. Fraser ATTORNEY United States Patent 3,356,884 ELECTRODE STARTING ARRANGEMENT HAV- ING A COILED HEATING ELEMENT CON- NECTED TO THE RETROVERTED PORTION OF THE ELECTRODE Walter J. Decker, North Bergen, and Hugh D. Fraser, West Caldwell, N.J., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 30, 1964, Ser. No. 379,110 6 Claims. (Cl. 313-212) ABSTRACT OF THE DISCLOSURE Improved electrode-starting arrangement for a discharge device wherein preferably one electrode is formed as an elongated member having a retroverted portion with one end portion of a fine wire heater coil fitted thereover for electrical contact and support. A shorter elongated member is positioned near the retroverted elongated member and the other end portion of the fine wire coil is fitted over and supported by this shorter elongated member. Lead-in conductors connect to the elongated members. The other device electrode may comprise a single elongated retroverted member with a fine wire coil fitted thereover, or both device electrode arrangements may incorporate the fine wire heater coil.

This invention relates to discharge devices and, more particularly, to discharge devices of the so-called additive type which incorporate improved electrode structures.

It is known to modify high-pressure, mercury-vapor discharge lamps by including additive materials, and particularly selected metallic iodides, in the arc tube. In the usual operation of such lamps, the mercury, which is fully vaporized, establishes the proper loading or voltage drop across the lamp and the additive iodides improve the color and luminous output of the discharge. Such socalled additive lamps are generally disclosed in Illuminating Engineering, June 1963, article entitled, Higher Efficiency Light Source Through Use of Additives to Mercury Discharge.

The usual high-pressure, mercury-vapor lamp incorporates electrodes which include an electron-emissive material, such as a thorium sliver or other emissive materials carried within a tungsten coil. It has been found that the additive materials react with the electron-emissive materials forming undesirable compounds which rapidly deplete the emission material and interfere with the proper operation of the lamp. In addition, the starting voltage required to strike an are between the electrodes of the additive device is initially relatively high and tends to increase throughout life. This can result in the lamp being classed as a premature failure.

In copending application of Hugh D. Fraser and Melvin C. Unglert, S.N. 379,109, filed concurrently herewith, titled, Electric Discharge Lamp, and owned by the present assignee, now Patent No. 3,307,069, is disclosed a starting arrangement for discharge lamps wherein a heating element within the arc tube is adapted to be selfresistance heated and is positioned proximate one of the operating electrodes. This permits the use of operating electrodes which consist essentially of tungsten. While this discharge lamp can'use various electrode constructions,

3,356,884 Patented Dec. 5, 1967 ICC the electrode constructions disclosed herein are particularly adapted for use with such a lamp It is the general object of this invention to provide an improved arc-discharge device which incorporates a solid electrode with a fine wire overwind and consists essentially of tungsten, and which electrode has a heating element formed as an integral part thereof to facilitate starting.

It is a further object to provide an improved arc-discharge device which incorporates a solid electrode with a fine wire overwind and consists essentially of tungsten, wherein the arc will quickly stabilize with respect to the electrode and thus improve the performance of the device.

The aforesaid objects of the invention, and other objects which will become apparent as the description pro-. ceeds, are achieved by providing an arc-discharge device wherein one electrode comprises a relatively fine wire, coiled tungsten member which has a coiled-coil barrel portion with coiled legs extending from each end thereof. Two solid elongated tungsten members fit tightly into the leg portions of the fine coil and one end of each of the tungsten members is embedded in one seal of the are tube. One of the tungsten members is longer than the other and has an extending extremity which is retroverted generally toward but is spaced from the proximate seal portion of the envelope. The portion of this electrode which projects furthest into the arc tube is thus formed as a curved, solid tungsten member which has a tightly fitting tungsten coil thereabout, with the coiled-coil barrel portion positioned intermediate this retroverted portion and the proximate seal of the arc tube. Preferably the other electrode is formed as a single, solid, elongated tungsten rod, the inwardly extending extremity of which is retroverted generally toward but spaced from that seal of the envelope which is proximate thereto. About the curved retroverted portion of this solid rod is positioned a tightly fitted, relatively fine wire tungsten coil.

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

FIGURE 1 is a sectional elevational view of a preferred lamp embodiment which incorporates the improved electrodes of the present invention;

FIG. 2 is a sectional elevational view of the arc tube portion of the lamp as shown in FIG. 1, illustrating in detail the electrodes as sealed into and positioned in the arc tube;

FIG. 3 is a view showing the electrode-heater element before incorporation into the arc tube;

FIG. 4 is a view showing the other electrode before incorporation into the lamp; and

FIG. 5 illustrates an alternative embodiment of arc tube wherein both electrodes have heating elements which form a part thereof.

With specific reference to the form of the invention illustrated in the drawings, the lamp 10 generally comprises a radiation-transmitting, sealed inner quartz envelope or are tube 12 having seals at either end thereof, with electrodes 14 and 16 disposed proximate the arc tube seals and operable to sustain a vapor discharge therebetweeu. For operation with the power input of 400 watts, the arc tube 12 encloses a volume of cc., a predetermined charge of mercury 18 is included in the arc tube 12 in amount of 122 milligrams and a predetermined amount of selected additive material such as 5 milligrams of thallium iodide 20, 15 milligrams of sodium iodide 22 and 10 milligrams of thallium metal 23 are also included within the arc tube 12. A small charge of inert ionizable starting gas, such as argon at a pressure of 20-25 millimeters, completes the discharge-sustaining filling.

A radiation-transmitting, sealed, outer envelope 24 is spaced from and surrounds the arc tube 12, and electrical lead-in conductors are sealed through both the inner envelope 12 and the outer envelope 24 and serve to electrically connect the operating electrodes 14 and 16 to a power source. The volume between the outer envelope 24 and the arc tube 12 preferably encloses a hard vacuum, although a nitrogen fill can be used.

The ends of the arc tube 12 have provided thereabout metallic end caps or heat shields 26. Aluminum silicate fiber or similar material is desirably packed intermediate the end caps 26 and the arc tube 12, in order to provide a good heat insulation effect and prevent condensation of the additive material at the ends of the arc tube. The arc tube 12 is supported within the outer envelope 24 by a conventional supporting frame 28. Conventional ribbon seals 30 facilitate making electrical connection through the arc tube.

The electrode 16 is fabricated as an electrode-heating element and the heater element end thereof electrically connects through a switching or bimetal means 32, in order to facilitate starting of the device, as described in detail in the aforementioned Patent No. 3,307,069. One end of the bimetal 32 connects through the arc tube frame 28 and the base member 34 to a conventional power source and the other end of the bimetal 32 is permanently connected through an insulated flexible leadin conductor 36 to the electrode 14.

The foregoing lamp is subject to considerable modification. For example, the quartz as used in the arc tube can be replaced by other refractory, light-transmitting material such as polycrystalline alumina. Also, other additive iodides can be used to replace those as specified and the iodides can be replaced by bromides or other halides, as is known. Lamps which are intended to be operated at other than 400 watts input will vary considerably with respect to size, amount of discharge-sustaining filling. etc., and the foregoing detailed specific example is not intended to be limiting.

The preferred arc tube embodiment which incorporates the present electrode structure is shown in greater detail in FIG. 2. The arc tube has seals 38 and 38a at each end thereof and the electrodes 14 and 16 are operatively positioned within the arc tube 12 proximate each of the respective envelope seals 38 and 38a. The electrode 16 consists essentially of tungsten and comprises a continuous, relatively fine wire, coiled tungsten member having a coiled-coil barrel portion 40 with coiled legs 42 and 43 extending from each end thereof. There are also provided two solid elongated members 44 and 46 which consists essentially of tungsten and which each have one end portion embedded in the proximate seal 38a of the arc tube. One of the elongated members 44 is longer than the other member 46 and extends within the arc tube toward the other electrode 14. The extending extremity of the elongated member 44 is retroverted generally toward but spaced from the proximate seal 38a of the arc tube and that portion which projects furthest toward the electrode 14 is formed as a curved, solid tungsten body 48 having the tightly fitting coil leg 42 thereabout. The coiled-coil barrel portion 40 is positioned intermediate the curved portion 48 and the proximate seal 38a. In the specific embodiment as shown, a substantial portion of the coil leg 43 is embedded in the seal 38a. If desired, only the solid tungsten member 46 need be embedded in the seal 38a.

The other electrode 14 consists essentially of tungsten and is operatively positioned within the arc tube proximate the seal 38. This electrode comprises a relatively fine wire tungsten coil 50 and a solid elongated tungsten rod 52. The rod 52 has one end portion thereof embedded in the seal38 and the other end portion of the rod 52 tightly fits into the tungsten coil 50. The rod 52 extends toward the electrode 16 with the extending extremity retroverted generally toward but spaced from the seal 38. The portion of the electrode 14 which projects furthest toward the electrode 16 is thus formed as a curved, solid tungsten rod portion 54 having the tungsten coil 50 tightly fitting thereabout.

Lead-in conductors connect to the electrodes 14 and 16 through the conventional ribbon seals 30. The electrode structure 16 is shown in greater detail in FIG. 3, which illustrates the electrode assembly before incorporation into the arc tube. As a specific example, the solid tungsten member 44 has a diameter of 30 mils and the solid tungsten member 46 has a diameter of 15 mils. The overwound tungsten coil is formed of wire having a diameter of 12 mils. The primary winding comprising the coil legs 42 and 43 has an interior coil diameter of 33.0 mils wound with 70 turns per inch. The coiled-coil barrel portion 40 is formed of three secondary winding turns with an in terior barrel diameter of 60 mils, wound with 13 turns per inch. After this electrode assembly is sealed into the arc tube, the projecting portions 56 of the hairpin-shaped assembly are cut away.

In FIG. 4 is shown the electrode 14 before incorporation into the arc tube. The fine wire tungsten overwind 50 has a diameter of 1.50 mils and is wound with 580 turns per inch. The solid rod 52 has a diameter of 30 mils. After this electrode assembly is incorporated into the arc tube, the projecting portions 56a of the hairpin-shaped assembly are cut away. The specific examples for the electrodes 14 and 16 as detailed hereinbefore are subject to considerable modification regarding wire diameters and coil pitch.

An alternative arc tube embodiment is shown in FIG. 5 wherein both ends of the arc tube 12a incorporate electrode-heating elements 16, as specified hereinbefore. With such a construction, the lamp can be started at still lower voltages by heating at both ends of the arc tube, preliminary to applying the arc-initiating potential between the electrodes. In other respects, this are tube embodiment is similar to the preferred embodiment as shown in FIG. 2.

When the potential is initially applied to the lamp, the bimetal 32 electrically connects directly to the embedded leg 43 of the heating element and the initial heating potential is applied directly across the electrode-heating element 16. The coiled-coil heating element 40 rapidly heats to an incandescent status to heat the lamp. As soon as the bimetal is heated, it is electrically disconnected from the heating element 40 and as a consequence, the potential is applied between the electrodes 14 and 16. Since the retroverted portion of the electrode 16 projects furthest into the arc tube body portion, the are quickly switches from the heater element 40 to the retroverted portion. The electrode 14 and the retroverted portion 48 0f the electrode 16 each provide for a very stable arc because of the fine wire tungsten overwind thereabout, which facilitates heating a localized spot on the solid tungsten members. Without the fine wire overwind, the arc would be quite unstable. If the solid tungsten portions which carry the overwind were eliminated, the fine wire would overheat and burn out.

When an additive lamp as shown in FIG. 1 is operated in conjunction with a conventional ballast and a starting circuit and incorporates the improved electrode structures of the present invention as shown in detail in FIG. 2, the starting voltage averages less than volts. If heater elements are provided at both ends of the arc tube, as in the embodiment shown in FIG. 5, the average starting voltage will be even lower. In either case, the starting voltage is substantially constant throughout the life of the device.

It will be recognized that the objects of the invention have been achieved by providing an improved arc-discharge device, particularly of the additive type, which incorporates improved electrode structures which facilitate starting and improve the stability of the arc.

While best embodiments of the invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

We claim as our invention:

1. An arc-discharge device comprising:

(a) an elongated radiation-transmitting envelope having a seal at each end and containing a predetermined amount of discharge-sustaining filling, and an electrode consisting essentially of tungsten and operatively positioned within said envelope proximate each said envelope seal, one of said electrodes comprising:

(1) a relative fine wire coiled tungsten member having a barrel portion with legs extending from each end thereof, and two solid elongated tungsten members,

(2) each of said solid elongated members having one end portion embedded in the proximate seal of said envelope with the other end portion of each of said solid elongated members tightly fitting into the legs of said coiled member,

(3) one of said solid elongated members being longer than the other of said solid elongated members and extending toward said other electrode, the extending extremity of said one solid elongated member retroverted generally toward but spaced from the proximate seal of said envelope with the portion of said one electrode which projects furthest toward said other electrode formed as a curved solid tungsten member having one of said legs forming a tightly fitting tungsten coil thereabout, and

(4) said barrel port-ion positioned intermediate said retroverted portion of said one solid elongated member and the proximate seal of said envelope; and

(b) lead-in conductors sealed through said envelope seals and individually electrically connected to said solid elongated members and said other electrode.

2. The device as specified in claim 1 wherein, said legs are each formed as a single coil and said barrel portion is formed as a coiled-coil.

3. An arc-discharge device comprising:

(a) an elongated radiation-transmitting envelope having a seal at each end and containing a predetermined amount of discharge-sustaining filling, one electrode consisting essentially of tungsten and operatively positioned within said envelope proximate one of said envelope seals, and an other electrode consisting essentially of tungsten and operatively positioned within said envelope proximate the other envelope seal, said other electrode comprising:

(1) a relative fine wire tungsten coil and a solid elongated tungsten rod,

(2) said solid elongated rod having one end portion embedded in said other envelope seal with the other end portion of said solid elongated rod tightly fitting into said tungsten coil,

(3) said solid elongated rod extending toward said one electrode, the extending extremity of said solid elongated rod retroverted generally toward but spaced from said other envelope seal with the portion of said other electrode which projects furthest toward said one electrode formed as a curved solid tungsten rod having said tungsten coil tightly fitting thereabout; and

(b) lead-in conductors sealed through said envelope seals and individually electrically connected to said one electrode and said solid elongated rod.

4. An arc-discharge device comprising:

(a) an elongated radiation-transmitting envelope having a seal at each end and containing a predetermined amount of discharge-sustaining filling, and an electrode operatively positioned within said envelope proximate each said envelope seal, one of said electrodes consisting essentially of tungsten and comprising:

(1) a continuous relatively fine wire coiled tungsten member having a coiled-coil barrel portion with coiled legs extending from each end thereof, and two solid elongated tungsten members,

(2) each of said solid elongated members having one end portion embedded in the proximate seal of said envelope with the other end portion of each of said solid elongated members tightly fitting into the coiled legs of said continuous coiled member,

(3) one of said solid elongated members being longer than the other of said solid elongated members and extending toward said other electrode, the extending extremity of said one solid elongated member retroverted generally toward but spaced from the proximate seal of said envelope with the portion of said one electrode which projects furthest toward said other electrode formed as a curved solid tungsten member having a tightly fitting tungsten coil thereabout, and t (4) said coiled-coil barrel portion positioned intermediate said retroverted portion of said one solid elongated member and the proximate seal of said envelope;

(b) said other electrode consisting essentially of tungsten and comprising:

(1) a relatively fine wire tungsten coil, and a solid elongated tungsten rod,

(2) said solid elongated rod having one end portion embedded in the proximate seal of said envelope with the other end portion of said solid elongated rod tightly fitting into said tungsten coil,

(3) said solid elongated rod extending toward said one electrode, the extending extremity of said solid elongated rod retroverted generally toward the proximate seal of said envelope with the portion of said other electrode which projects furthest toward said one electrode formed as a curved solid tungsten rod having said tungsten coil fitting tightly thereabout; and

(c) lead-in conductors sealed through said envelope seals and individually electrically connected to said solid elongated members and said solid elongated rod.

5. An arc-discharge device comprising:

(a) an elongated radiation-transmitting envelope having a seal at each end and containing a predetermined amount of discharge-sustaining filling, and an electrode consisting essentially of tungsten and operatively positioned Within said envelope proximate each said envelope seal, each of said electrodes comprising:

(1) a continuous relatively fine wire coiled tungsten member having a coiled-coil barrel portion with coiled legs extending from each end thereof, and two solid elongated tungsten members,

(2) each of said solid elongated members having one end portion embedded in the proximate seal of said envelope with the other end portion of each of said solid elongated members tightly fitting into the coiled legs of said continuous coiled member,

(3) one of said solid elongated members being longer than the other of said solid elongated members and extending toward the other of said electrodes, the extending extremity of said one solid elongated member retroverted generally toward that seal of said envelope which is proximate thereto with the portion of each said electrode which projects furthest toward the other of said electrodes formed as a curved solid tungsten member having a tightly fittingtungsten coil thereabout, and

7 (4) said coiled-coil barrel portion positioned intermediate said retroverted portion of said one solid elongated member and that seal of said envelope which is proximate thereto; and (b) lead-in conductors sealed through said envelope seals and individually electrically connected to each said solid elongated members of said electrodes.

6. The arc-discharge device as specified in claim 1, wherein the portion of said leg of said fine wire coiled tungsten member which fits onto the shorter of said solid elongated members is embedded in the proximate seal of said envelope.

* References Cited UNITED STATES PATENTS 1,749,780 3/1930 Reritschler 313-337 X 5 2,263,171 11/1941 Hays et al 31547 3,013,175 12/1961 Waymouth et a1. 313-109 X DAVID J. GALVIN, Primary Examiner.

10 JAMES W. LAWRENCE, Examiner.

S. A. SCHNEEBERGER, Assistant Examiner. 

1. AN ARC-DISCHARGE DEVICE COMPRISING: (A) AN ELONGATED RADIATION-TRANSMITTING ENVELOPE HAVING A SEAL AT EACH END AND CONTAINING A PREDETERMINED AMOUNT OF DISCHARGE-SUSTAINING FILLING, AND AN ELECTRODE CONSISTING ESSENTIALLY OF TANGSTEN AND OPERATIVELY POSITIONED WITHIN SAID ENVELOPE PROXIMATE EACH SAID ENVELOPE SEAL, ONE OF SAID ELECTRODES COMPRISING: (1) A RELATIVE FINE WIRE COILED TUNGSTEN MEMBER HAVING A BARREL PORTION WITH LEGS EXTENDING FROM EACH END THEREOF, AND TWO SOLID ELONGATED TUNGSTEN MEMBERS, (2) EACH OF SAID SOLID ELONGATED MEMBERS HAVING ONE END PORTION EMBEDDED IN THE PROXIMATE SEAL OF SAID ENVELOPE WITH THE OTHER END PORTION OF EACH OF SAID SOLID ELONGATED MEMBERS TIGHTLY FITTING INTO THE LEGS OF SAID COILED MEMBER, (3) ONE OF SAID SOLID ELONGATED MEMBERS BEING LONGER THAN THE OTHER OF SAID SOLID ELONGATED MEMBERS AND EXTENDING TOWARD SAID OTHER ELECTRODE, THE EXTENDING TOWARD SAID OTHER ELECELONGATED MEMBER RETROVERTED GENERALLY TOWARD BUT SPACED FROM THE PROXIMATE SEAL OF SAID ENVELOPE WITH THE PORTION OF SAID ONE ELECTRODE WHICH PROJECTS FURTHEST TOWARD SAID OTHER ELECTRODE FORMED AS A CURVED SOLID TUNGSTEN MEMBER HAVING ONE OF SAID LEGS FORMING A TIGHTLY FITTING TANGSTEN COIL THEREABOUT, AND (4) SAID BARREL PORTION POSITIONED INTERMEDIATE SAID RETROVERTED PORTION OF SAID ONE SOLID ELONGATED MEMBER AND THE PROXIMATE SEAL OF SAID ENVELOPE; AND (B) LEAD-IN CONDUCTORS SEALED THROUGH SAID ENVELOPE SEAL AND INDIVIDUALLY ELECTRICALLY CONNECTED TO SAID SOLID ELONGATED MEMBERS AND SAID OTHER ELECTRODE. 